function Parent() {
  this.name = 'Tom'
  this.like = [1, 2]
  this.girlfriend = {
    n: 1
  }

}

Child.prototype = new Parent()

function Child(age) {
  this.age = age
}

let child1 = new Child(18)

// let child2 = new Child()

// child1.name = 'Jerry'  // no
// child1.like.push(3)   // yes
// child1.girlfriend.n = 2  // yes
// child1.girlfriend = {n: 2}  // no

// console.log(child1.girlfriend.n); 
// console.log(child2.girlfriend.n); 